Chapter 7 2018/2019

a) A sample of 0.214 g of unknown monoprotic weak acid, HA was dissolved in 25.00 mL of water and titrated with 0.1 M NaOH. The acid required 27.40 mL of the base to reach the equivalent point.      

i. Determine the molarity of the acid.    

[2 Marks] 

ii. Calculate the pH of the solution if 40 mL NaOH is added to the acid solution.     

[6 Marks] 

iii. Explain qualitatively the pH of the solution at equivalent point      

[4 Marks] 

b) Magnesium arsenate, Mg3(AsO4)2, is used as an insecticides and it is toxic to humans. Calculate the solubility Mg3(AsO4)2 of in water at 25oC. [Given: Ksp Mg3(AsO4)2 = 2.2 x 10–20] 

[5 Marks]